Like a flip book, animation on screen is created by drawing an image, then drawing a slightly different image, then another, and so on. The illusion of fluid motion is created by persistence of vision. When a set of similar images is presented at a fast enough rate, our brains translate these images into motion.
To create smooth motion, Processing tries to run the code inside
draw() at 60 frames each second. A frame is one trip through the
draw() and the frame rate is how many frames are drawn each second. Therefore, a program that draws 60 frames each second means the program runs the entire code inside
draw() 60 times each second.
To confirm the frame rate, run this program ...